How much does the engine pylon on modern jets affect the airflow coming out of the engine?
What's the actual pylon's effect on airflow?
Are there any sections inside the engine (besides the mounting points) designed considering the disturbance the pylon creates on the airflow?

After taking into account the different types of engine cowlings & exhaust pipes, and the different pylon designs and mounting configurations ......... my guess would be that the affect of disturbance on both the hot core gases and the by-pass airflow (as mentioned in your topic's title), would be between none and .000005%.

I'm going to try to read your mind a bit!

If you were to look at the first 2 photos of the B747 & B767 below, you might be wondering about whether or not the pylon affects the bypass airflow because the by-pass air exits the engine beside the pylon .... several feet ahead of the pylon's trailing edge. In this case, the pylon may actually help the by-pass airflow (not disturb it), by straightening it out a bit ... just a guess. (engine types anyone? - RB211, PW4000, CFM, GE)

The situation in the case above wouldn't be an issue on airliners with engines that have one full length cowling with both the by-pass air and hot core gases exiting from the same single jet pipe ....... like the engines on the B757 & A320 in these 2 photos. (engine types anyone? - RB211, PW4000, CFM, GE)

>> You asked ......... "Are there any sections inside the engine (besides the mounting points) designed considering the disturbance the pylon creates on the airflow?"

I don't know, but I don't think so. On a side note, the jet engines on MD-80s have guide vanes inside the intake infront of the fan which I believe are for re-directing the intake air to make the fan more efficient ..... but that's got nothing to do with your questions. Sorry!

Finally, if by saying ..."the disturbance the pylon creates on the airflow", you are talking about any "turbulence" that is created by the pylons, on any airliner regardless of the engine/pylon mounting design, then I would have to say ...... I doubt it!

By the time any turbulence caused by the pylon reached the by-pass & hot core airflow behind the engine, the airflow's work (thrust!) would have already been done ...... thus there would be no disturbance affect.

The Bypass air on modern engines actually travels through 2 "C-ducts", which as im sure you can imagine are C shaped. This means that there are two areas, such as ( ) the top and the bottom where there is no bypass airflow.